1. Field of the Disclosure
The present invention relates generally to flame retardant electronic circuitry packaging. More specifically, the methods and compositions of the present invention are directed to flexible, aqueous-processible, photoimagable, multi-layer coverlay compositions having little, if any, halogen (compared to conventional flame retardant coverlays), due at least in part to the use of a phosphorus based chemistry in at least one layer of the multi-layer coverlay.
2. Description of Related Art
Photosensitive coverlay compositions are discussed broadly in U.S. Pat. No. 5,536,620 to Dueber et al. In many coverlay applications, flame retardancy can be important. Although halogenated materials have been used to provide flame retardancy to coverlays, environmental concerns have increasingly pressured manufacturers to make halogen-free flame retardant coverlay materials. Phosphorus is know to provide flame retardancy, but phosphorus can be problematic, e.g., cause undesirable phosphorus “bleed” and/or poor flexibility.